Field
This disclosure relates generally to a local oscillator signal generator, and more specifically, to a local oscillator signal generator with VDD/GND harmonic current rejection.
Background
Due to stringent phase noise, slew rate, and duty cycle requirements, a local oscillator (LO) circuit can draw large current in the range of tens of milliamps. Thus, an LO circuit that operates rail to rail can generate a strong harmonic current ripple (going from the ground voltage (GND) to a maximum voltage (VDD)) at multiple LO frequencies. Such a current ripple at LO harmonic frequencies can cause interference issues. For example, an LO signal appearing at a low noise amplifier (LNA) input can become an in-band jammer. In another example involving carrier aggregation (CA), a frequency of a second receive LO signal (N*FRxlo2) can mix with a frequency of a first transmit LO signal (M*FTx1) to generate a jammer tone falling into and de-sensing the receiver in-band channel (Rx1). Further, at high frequencies, a filtering technique may not be reliable because it may be sensitive to the ground inductance and can be highly layout and floor plan dependent. Therefore, it is desirable to reduce the LO harmonic current ripple.